Identify the incorrect statement.

• A
  Myelinated nerve fibers are found in spinal and cranial nerves.
• B
  Unmyelinated nerve fiber is enclosed by a Schwann cell that does not form a myelin sheath around the axon.
• C
  In a resting state,the axonal membrane is more permeable to potassium ions $(K^+)$ and nearly impermeable to sodium ions $(Na^+)$.
• D
  The axonal membrane is highly permeable to negatively charged proteins present in the axoplasm.